The present invention relates to an improved pre-filter for removing larger lint particles from an air stream prior to filtration of smaller particles, dust, and other contaminants by a conventional filter apparatus, and to a rotating nozzle for use in cleaning filter screens.
Textile manufacturing plants generate a large quantity of lint, i.e., fiber pieces, which must be removed from the work environment to ensure worker comfort and safety.
Removal is normally achieved by withdrawing lint containing air from the work area and conveying it through a filtration system where the lint is collected on filters. An example of the apparatus used is to be found in U.S. Pat. No. 5,114,444 to Stuble. Normally, the filtration apparatus is comprised of a housing enclosing a plurality of filters, e.g., of the drum or bag type, and a fan to convey air through the filters. When air passes through the filter surface, lint is deposited on the filter. Periodically, the filter surface is vacuumed or back-flushed to remove lint, which is collected by a lint separator.
A concern of air filtration systems collecting large particles, such as lint, heavy sawdust and the like, is that larger particles collecting on the filter surface, clog the surface too quickly, and thus reduce the filtration efficiency. Also, at least in the case of lint, the larger lint particles are reusable, and it is helpful to remove them separately from the smaller unusable lint particles and dust. One approach to addressing this concern is to first pass the lint containing air through a screen (pre-filter) which will collect larger particles. U.S. Pat. No. 4,364,755 to Ferri, for example, shows an apparatus including a circular screen or disk having relatively large pores or openings (100-250 microns) attached to the incoming or intake end of a filter drum. Air passes through the screen prior to entering the drum which contains a higher mesh filter (1-15 microns). Particles collecting on the screen, which is caused to rotate past a stationary nozzle, are removed by the nozzle adjacent the screen surface.
The disadvantage of this system, however, is that the screen must rotate to effect cleaning. The screen is relatively large and the rotation of such a large screen presents problems, such as maintenance of an air seal, energy usage, and the like. Also since the screen rotates at the same speed as the suction apparatus which cleans the inside of the drum filter, there is no independent control over the speed of movement of the screen relative to the vacuum arm. Thus effectiveness of the lint removal from the screen is diminished.
The objectives of the present invention are to provide a method and apparatus for efficiently removing larger lint particles from an air stream prior to filtration of the dust and finer particles from the air stream, which permits improved control of the prefiltration operation independent of the subsequent filtration of the fines from the airstream.
Further, although the ensuing description is directed to a system for lint removal, the same concepts apply to other types of filters where the size of the contaminating particles varies through a wide range, and it is necessary or desirable to pre-filter and collect larger particles upstream of the conventional filtration operation.
Even further, the present invention includes a unique suction nozzle that rotates about an axis, thus providing effective cleaning of a large surface area.